Hydrogen absorption in oxide-supported palladium nanocrystals

Substantial hydrogen absorption in nanometer-sized palladium crystallites on a thin film alumina support is observed at 90-350 K under low H-2 pressure conditions (<2 x 10(-3) Pa) by H-1 (N-15, alpha gamma)C-12 nuclear reaction analysis. The enthalpy of H solution varies with the absorbed H content and with -(0.28 +/- 0.02) eV/H exceeds that of bulk Pd at H/Pd ratios below 0.20. By resolving absorbed H from surface-adsorbed H, this enhanced H stability is identified as an intrinsic volume property of the small crystallites rather than being associated with particular binding sites on or near their surfaces.